1. Technical Field
The present invention relates to an anode for a secondary battery and a secondary battery.
2. Background Art
Because of the popularization of a mobile terminal such as a cell phone, a laptop PC (personal computer) and the like, the role of a battery has been important as its power source. This battery requires the features that it has small size, lightweight and a high capacity and it is not easily deteriorated even if charge and discharge are repeated. A lithium secondary battery is optimal for the above-mentioned application because of its high operation voltage and high energy density. In the lithium secondary battery, as a cathode material, the material whose chief ingredient is LiCoO2 or manganese spinel is mainly used, and as an anode material, a carbon material such as graphite is typically used. In recent years, these materials are used to obtain the performance substantially close to the theoretical capacity (372 mAh/g in the case of the graphite). In order to make the energy density higher, the material that has high theoretical discharge capacity is used to try various ideas.
For example, a conventional technique, disclosed in Japanese Laid Open Patent Application JP-A 2000-215887, tries to cover the surfaces of metal particles with carbon layer and use the particle as the anode material in order to attain the properties of a high capacity and a high cycle, the metal particles can form a lithium alloy.
Also, a conventional technique, disclosed in Japanese Laid Open Patent Application JP-A-Heisei 9-259868, adds aluminum, lead and silver with small particle diameters to the carbon material as the charge and discharge assistant of lithium ions in order to attain the higher capacity.
However, the techniques disclosed in the above-mentioned gazettes have the following problems.
Firstly, the sufficiently high operation voltage cannot be attained. If the anode is manufactured by using metal particles such as Si and the like as the chief ingredient, the operation voltage is strongly influenced by the plateau at the high potential unique to the metal. This leads to the drop in the operation voltage of the battery.
Secondly, since a homogeneous electric field strength cannot be obtained between the cathode and anode, the sufficiently stable operation cannot be obtained. If the particles of Li absorption metal are added to the carbon so that they are interspersed inside the electrode, the inhomogeneous resistance and Li absorption amount of those sections bring about the inhomogeneous application voltage and current amount, which causes the peeling and the like.
Thirdly, the deterioration in the capacity is severe in association with the cycle. The Li absorption metal is larger in capacity and greater in volume change than the carbon, in association with the charge and discharge. Thus, the electric contact between the Li absorption metal and the carbon particles is reduced with the cycle, and the Li absorption metal cannot contribute to the charge and discharge.
In relation to the above-mentioned description, a non-aqueous secondary battery is disclosed in Japanese Laid Open Patent Application JP-A 2000-182671. This non-aqueous secondary battery in the conventional art has: a sheet (an anode sheet) including the anode material that can absorb and discharge the lithium; a sheet (a cathode sheet) including a cathode electrode active material; and a non-aqueous electrolyte. The cathode active material is the metallic oxide or metallic sulfide which includes at least one kind of an atom selected from vanadium, copper, iron, titanium, molybdenum and chrome and does not include the lithium contributing to the charge and discharge preliminarily and substantially. The metallic foil which mainly includes the lithium is preliminarily stuck to the anode sheet. Also, the non-aqueous electrolyte is the gel electrolyte including organic polymer, aprotic solvent and ammonium salt or alkali metal or alkali-earth metal salt. The metallic foil mainly containing the lithium is stuck on the combination layer of the anode sheet on which the anode material is coated. Or, it is stuck on the anode collector metal on the surface which is not faced to the cathode sheet. The anode sheet is configured as the multi-layer which has: the layer mainly containing the anode material that can absorb and discharge the lithium; and the assistant layer containing the insoluble particles of at least one layer.
Also, a secondary battery is disclosed in Japanese Laid Open Patent Application JP-A 2000-311681. The anode material of this conventional lithium secondary battery includes the particles whose chief ingredient is the amorphous Sn-A-X alloy with non-stoichiometric ratio composition. In the above-mentioned equation, the A indicates at least one kind of a transition metal, and the X indicates at least one kind selected from a group consisting of O, F, N, Mg, Ba, Sr, Ca, La, Ce, Si, Ge, C, P, B, Bi, Sb, Al, In, S, Se, Te and Zn. Here, the X may not be included. Also, in the atom number in the respective atoms in the above-mentioned equation, there is the relation of Sn/(Sn+A+X)=20˜80 atom %.
A non-aqueous electrolyte secondary battery is disclosed in Japanese Laid Open Patent Application JP-A 2001-68112. The anode active material for the non-aqueous electrolyte secondary battery in this conventional art is composed of the particles having three phases or more with regard to material organization, and at least two phases are the phase that absorbs the lithium, and at least one phase is the phase that does not absorb the lithium. The two phases absorbing the lithium have the composition represented by an equation M1αM2 (0≦α<3) and M3αM4 (α<a), and the phase that does not absorb is represented by M5. The M1 and the M3 are at least one kind of an element selected from a group consisting of Na, K, Rb, Cs, Ce, Ti, Zr, Hf, V, Nb, Ta, Ca, Sr, Ba, Y, La, Cr, Mo, W, Mn, Tc, Ru, Os, Co, Rh, Ir, Ni, Pd, Cu, Ag and Fe, the M2 and the M4 are at least one kind of an element selected from a group consisting of Al, Ga, In, Si, Ge, Sn, Pb, Sb and Bi, and the M5 is a simplex or compound that is x≦0.05 when the composition at the time of the Li absorption is represented by an equation LixM5.
Also, a non-aqueous electrolyte secondary battery is disclosed in Japanese Laid Open Patent Application JP-A 2001-76719. The anode material for the non-aqueous electrolyte secondary battery in this conventional art, is represented by the equation (1): M1aM2, and all or a part of the surface of the particle having the A-phase of the composition satisfying 0≦a≦5 is represented by the equation (2): M1′bM2′c, and it is covered with the B-phase of the composition satisfying c=1 or c=0, here, if c=1 then a<b. The M1 and the M1′ are the elements selected from an (m1) group consisting of Na, K, Rb, Cs, Ce, Ti, Zr, Hf, V, Nb, Ta, Ca, Sr, Ba, Y, La, Cr, Mo, W, Mn, Tc, Ru, Os, Co, Rh, Ir, Ni, Pd, Cu, Ag and Fe, and the M2 and the M2′ are the elements selected from an (m2) group composed of Al, Ga, In, Si, Ge, Sn, Pb, Sb and Bi. Then, 50% or more of the surface of the particle having the A-phase is covered with the B-phase. The concentration of at least one kind of the element selected from the (m1) group is being reduced gradually from the surface to the inside.
Also, a non-aqueous electrolyte secondary battery is disclosed in Japanese Laid Open Patent Application JP-A 2001-243946. In the non-aqueous electrolyte secondary battery in this conventional art, the anode includes the anode material composed of composite particles in which the whole or part of the circumferential surface of the nuclear particle consisting of a solid phase A is covered with a solid phase B. The solid phase A includes at least one of silicon, tin and zinc as the configuration element, and the solid phase B is composed of solid solution or inter-metal compound of any of the silicon, the tin and the zinc which are the configuration elements of the solid phase A and at least one kind of the element (however, except for the configuration elements of the solid phase A and the carbon) selected from a group consisting of a group II element, a transition element, a group XII element, a group XIII element and a group XIV element in a periodic table, and the composite particle includes ceramic. The ceramic is made of at least one kind or more selected from a group consisting of SiC, Si3N4, Al2O3, TiC, TiB2, V2O3, ZrB2, HfB2, ZrO2, ZnO, WC and W2C.